This invention relates to annular aerodynamic windows and more particularly to flashlamps having plasma containment with an annular aerodynamic window.
Plasma light sources capable of producing radiation having a high intensity are desirable for use as flashlamps and for use as pumping sources for high power lasers. In prior art devices, such as the flashlamp disclosed by Van Ornum in U.S. Pat. No. 3,292,028, radiation having a high intensity is typically produced in a plasma generated by an electric discharge or arc in a high pressure gas contained within a cavity enclosed by an envelope of solid material which is transparent at the wavelength of the radiation produced. The envelope is typically of silica or quartz material. The high current electric arc or spark which produces the plasma is typically gas vortex-stabilized along an axis within a predetermined arc region between electrodes by means of a gas which is introduced tangentially into the cavity containing the discharge.
The utilization of a transparent material to contain the gas and to allow radiation to pass therethrough results in a limitation being imposed on the intensity of the radiation obtainable from the flashlamp. The intensity of the radiation is a function of the pressure of the gas contained within the transparent envelope and of the amount of electric current passing through the gas. The pressure of the gas is limited by the mechanical properties of the transparent envelope and the amount of electric current passing through the gas is limited by the ability of the envelope to conduct heat, generated by the discharge within the gas, to a heat sink without producing a temperature within the envelope sufficient to cause discoloration or deterioration of the optical or mechanical properties thereof. A further limitation is the heat generated within the envelope by the absorption of a portion of the radiation passing therethrough. Although various cooling means have been devised to enhance the removal of heat from the envelope, the utilization of an envelope of solid material results in a limitation in the operational characteristics of the flashlamp.
An additional problem of prior art devices is the limited lifetime of the envelope due to discoloration during operation caused in part by the deposition of electrode material thereon, deterioration due to the high intensity radiation incident thereon, and from deposition of seed material within the high pressure gas onto the envelope. The seed material is typically inserted into the gas to obtain spectral selectivity of the radiation.
The present invention utilizes a cylindrical aerodynamic window defined by an annular flow path to replace the envelope of solid material to overcome some of the difficulties of prior art devices. Aerodynamic windows have been utilized in prior art devices to provide transparent windows for passing high intensity radiation therethrough while maintaining a pressure differential across the window. Hausmann in U.S. Pat. No. 3,617,928 filed May 23, 1968, discloses an aerodynamic window for a gas dynamic laser and in U.S. patent application Ser. No. 862,708 filed Dec. 20, 1977 discloses a spatial filter having aerodynamic windows on both sides of the filter to allow a high power laser beam to pass therethrough. Prior art aerodynamic windows have been two dimensional.